Method for measuring the salt concentration of excess electrolyte in secondary battery cells

Abstract

When detecting the salt concentration of the excess non-aqueous electrolyte in a secondary battery cell by irradiating it with X-rays and measuring the transmission intensity, the cell is positioned so that the transmission distance of X-rays through the excess electrolyte in the cell remains constant between the X-ray source and the X-ray detector. [Solution] A cell is placed on a jig 5 with one corner at its lowest point, and the outer surface of the cell or its restraint plate is in contact with the claw portions 63a and 63b that protrude upward at the edges of the flat portions. The jig 5 consists of a first jig 51 which is a rectangular flat plate with an L-shaped projection 53 that protrudes vertically from one corner and is fastened to the sample stage 4 between the X-ray source 2 and the X-ray detector 3 by screws, and a second jig 60 which has a base portion 61 that abuts the inner surface of the L-shaped projection, and two flat plate portions 62a and 62b that extend diagonally upward from the portion between the two opposing edges and are oriented so that the plane direction is substantially parallel to the direction of X-ray propagation.

Description

Technical Field

[0004] , , , , , , ,

[0001] The present invention relates to a method for inspecting a secondary battery containing a non-aqueous electrolyte such as a lithium-ion battery, and more particularly to a method for inspecting the state of the electrolyte of a used secondary battery.

Background Art

[0002] In order to determine whether a secondary battery used in an electric vehicle such as a hybrid vehicle or an electric vehicle can be reused after being recovered, a method for inspecting the deterioration state of the secondary battery without destroying the secondary battery has been proposed. In Patent Document 1, X-rays or ultrasonic waves are irradiated onto the cells of a secondary battery, the transmittance is measured, and based on the measured transmittance, the surplus liquid amount of the non-aqueous electrolyte in the cell is calculated, and according to the calculated remaining liquid amount, it is proposed to determine whether the cell can be reused.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described in Japanese Patent Application No. 2023-175267 by the present applicant, the degradation state of a secondary battery is also reflected in the salt concentration of the excess non-aqueous electrolyte in the cell. Therefore, in order to more accurately evaluate the degradation state of the secondary battery, it is preferable to be able to measure this salt concentration as well. In this regard, the transmittance of X-rays in the excess non-aqueous electrolyte in a secondary battery cell changes depending on the salt concentration of the excess electrolyte. Therefore, the salt concentration of the excess electrolyte can be determined by detecting the X-ray transmission intensity when X-rays are irradiated into the excess non-aqueous electrolyte in the cell, and from the detected X-ray transmission intensity. At that time, the X-ray transmission intensity also changes depending on the transmission distance of the X-rays in the excess electrolyte (the longer the distance, the more the X-rays are absorbed by the excess electrolyte and the lower the transmission intensity). Therefore, in a device for measuring the X-ray transmission intensity of a cell, it is preferable to be able to position the cell so that the transmission distance of the X-rays in the excess electrolyte in the cell is always constant when the cell is placed between the X-ray source and the X-ray detector.

[0005] In view of the above circumstances, the main object of the present invention is to enable the arrangement of a cell such that, when irradiating the excess non-aqueous electrolyte in the cell with X-rays and detecting the salt concentration of the excess liquid from the transmission intensity, the transmission distance of X-rays in the excess liquid in the cell remains constant between the X-ray source and the X-ray detector. [Means for solving the problem]

[0006] According to the present invention, the above problem is solved by a method for detecting the salt concentration of the excess non-aqueous electrolyte in a secondary battery cell based on the amount of X-rays transmitted through the excess electrolyte irradiated onto the excess electrolyte, The process of placing a jig on a sample stage positioned between the X-ray source and the X-ray detector, The process of installing the cell on the jig, The process involves irradiating the cell with X-rays from the X-ray source and measuring the intensity of the X-rays that have passed through the excess liquid in the cell using the X-ray detector, A process for detecting the salt concentration of the excess liquid based on the measured X-ray intensity, Includes, The jig on which the cell is installed is A first rectangular flat jig fastened to the sample stage by screws, the first jig having an L-shaped projection formed perpendicular to the surface direction across two intersecting outer edges at one corner, A second jig having a base portion that abuts the inner surface of the L-shaped projection of the first jig, and two flat plate portions formed to extend diagonally upward from the portion between the two opposing edges of the base portion toward the upper part of each of the two edges, wherein the two flat plate portions are oriented such that their surface directions are substantially parallel to the direction of X-ray propagation, and claw portions are formed on the edges of the two flat plate portions that extend in a direction substantially perpendicular to the direction of X-ray propagation, with the claw portion projecting upward. Includes, In the process of setting the cell on the jig, when setting the cell on the second jig, the two intersecting edge surfaces of the cell at one corner are extended along each of the two flat plate portions of the second jig, and the outer surface of the cell perpendicular to the edge surface, or, when the cell is held between two restraining plates, the outer surface of one of the restraining plates is brought into contact with the claw portion, thereby making the one corner of the cell the lowest point, and maintaining a substantially constant transmission distance of the X-rays passing through the cell.

[0007] In the above configuration, the configuration of the X-ray source, X-ray detector, and sample stage placed between them may be the same as in the case of a system for inspecting the X-ray transmission intensity of a normal sample, as described in Patent Document 1. The secondary battery cell may be a normal, substantially rectangular secondary battery cell. By placing the cell on the sample stage with one corner facing downwards, as described in Patent Document 1, excess liquid accumulates in one corner, and when X-rays are irradiated there, the X-ray transmission intensity of the excess liquid is measured. The cell may be placed directly on the jig, or it may be placed in a state of compression and restraint by restraint plates on both sides, as described in Patent Document 1. In converting the salt concentration of the excess liquid in the cell from the X-ray transmission intensity of the cell, the X-ray transmission intensity may be measured using samples with various known salt concentrations, and the relationship between salt concentration and X-ray transmission intensity may be determined (a calibration curve may be created). Using this relationship, the salt concentration of a sample with an unknown salt concentration may be determined from the X-ray transmission intensity. The jig may be made of a material commonly used in this field, such as plastic or metal.

[0008] In the method of the present invention described above, by placing the jig on the sample stage and arranging the cells on the jig as described above, the cells can be arranged on the sample stage in substantially the same state with good reproducibility, such that one corner faces downwards. As shown in the experimental example described later, even if the same cells are rearranged, the salt concentration can be stably detected. [Effects of the Invention]

[0009] Thus, according to the method of the present invention, in a system for inspecting X-ray transmission intensity, the cell is always positioned in substantially the same state on the sample stage, and variations in the X-ray transmission distance in the cell are suppressed, thereby enabling stable detection of the salt concentration of the excess liquid in the cell. The method of the present invention may be advantageously used when determining whether or not a cell can be reused.

[0010] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the present invention. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1(A) is a schematic diagram of an X-ray inspection system for secondary battery cells to which the method of this embodiment is applied. Figure 1(B) is a schematic diagram of the change in the excess liquid salt concentration in the secondary battery cell with respect to the X-ray transmission intensity in the secondary battery cell in the method of this embodiment. Figures 1(C) and (D) illustrate how the transmission distance of X-rays passing through the cell changes depending on the inclination of the cell. [Figure 2] Figures 2(A) and 2(B) are schematic plan and side views of the first jig used in the method of this embodiment. [Figure 3] Figures 3(A) and 3(B) are schematic perspective and top views of the second jig used in the method of this embodiment. Figures 3(C) and 3(D) are schematic cross-sectional views of the claw portion formed on the inclined plane of the second jig, as seen from CC and DD in Figure 3(B), respectively. [Figure 4] Figure 4 is a schematic perspective view showing the second jig mounted on the first jig. [Figure 5] Figures 5(A) and (B) are schematic perspective views and schematic front views, respectively, of the cell set up on the first and second fixtures fixed to the sample stage, and the cell viewed from a direction perpendicular to the cell's surface. The cell is held between restraint plates. [Figure 6] Figure 6 shows the excess liquid salt concentration calculated from the X-ray transmission intensity measured each time the same cell was repositioned on the jig multiple times. [Explanation of symbols]

[0012] 1...X-ray inspection system, 2...X-ray source, 3...X-ray detector, 4...Sample stage, 5...Jig, 51...First jig, 52...Screw hole, 53...L-shaped projection, 60...Second jig, 61...Base, 61a...Corner of base, 62a, 62b...Inclined flat plate, 63a, 63b...Claw, S...Inspection sample, S1...Cell, S2, S3, S4...Restraint plate, S5...Load cell [Best Mode for Carrying Out the Invention]

[0013] While referring to the attached drawings below, the present invention will be described in detail with respect to several preferred embodiments. In the drawings, the same reference numerals indicate the same parts.

[0014] Configuration of an X-ray inspection system The X-ray inspection system used for detecting the salt concentration of the surplus liquid in the secondary battery cell according to the present embodiment may be any system as long as it can irradiate the sample with X-rays and measure the transmission intensity thereof. Briefly stated, as shown in FIG. 1(A), in the X-ray inspection system 1, an X-ray source 2 that emits X-rays and an X-ray detector 3 that receives the X-rays and detects the intensity are provided, and a sample stage 4 is arranged between them. In the case of the present embodiment, a jig 5 is installed on the sample stage 4, and a sample S, which is a secondary battery cell alone or a secondary battery cell sandwiched between two restraint plates, is arranged thereon (for sandwiching the secondary battery cell with the restraint plates, refer to Patent Document 1). Here, the secondary battery cell has a substantially rectangular flat plate shape, and as will be described in detail later, it may be arranged such that the wide surface of the cell faces substantially perpendicular to the traveling direction of the X-rays.

[0015] Detection of the salt concentration of excess liquid in the cell from the X-ray transmission intensity in the cell. In the present embodiment, based on the finding that the intensity of the X-rays transmitted through the portion where the surplus liquid has accumulated in the cell changes depending on the salt concentration of the surplus liquid, as also described in Patent Document 1 and Japanese Patent Application No. 2023-175267 mentioned above, the salt concentration of the surplus liquid is detected from the intensity of the X-rays (transmission intensity) irradiated and transmitted to the lower part of the cell. Typically, for example, for cells having surplus liquids with a plurality of known different salt concentrations, the X-ray transmission intensities are measured respectively, and as shown in FIG. 1(B), the surplus liquid salt concentration Cs is plotted against the X-ray transmission intensity Ix to create a calibration curve TL. For a sample with an unknown salt concentration, its X-ray transmission intensity is measured, and the value of the salt concentration corresponding to the measured value on the calibration curve TL is determined as the salt concentration of the sample.

[0016] Incidentally, in the configuration of the X-ray inspection system 1 described above, the transmission intensity of X-rays that pass through the cell also changes depending on the transmission distance of the X-rays within the cell. In this regard, as shown in Figure 1(C), the deviation δ from the transmission distance ΔL of the X-rays within the cell when the surface of cell C is tilted from the direction perpendicular to the direction of X-ray propagation, as shown in Figure 1(D), increases as the tilt angle θ increases. Furthermore, since X-rays from the X-ray source generally have unevenness in the plane perpendicular to the direction of propagation, the transmission intensity of the X-rays also changes if the position of the cell is shifted in a direction perpendicular to the direction of X-ray propagation, although this is not shown in the figure. Therefore, if there is variation in the position and orientation of the cell installed on the sample stage, the transmission intensity of the X-rays will also vary, and the salt concentration value calculated from the transmission intensity of the X-rays will also vary. Thus, as described above, when detecting the salt concentration of the excess liquid in the cell from the transmission intensity of X-rays that have passed through the cell, it is preferable that the cell be positioned on the sample stage in the same orientation and position as much as possible at all times.

[0017] Configuration of a jig that is placed on a sample stage and holds the cell. As described above, in order to ensure that the cells are always positioned in the same orientation and location on the sample stage, a jig 5 as shown in Figures 2 to 5 is used in this embodiment. More specifically, the jig 5 may consist of a first jig 51 as shown in Figure 2 and a second jig 60 as shown in Figure 3.

[0018] The first jig 51, as shown in Figure 2, is a rectangular flat plate-shaped member, and several screw holes 52 are appropriately formed to fasten it to the sample stage 4 with screws (not shown). In addition, for positioning the second jig 60 which is placed on the first jig 51, L-shaped protrusions 53 are formed that project perpendicular to the surface direction across two outer edges that intersect at one corner of the rectangular flat plate shape.

[0019] On the other hand, the second jig 60, as shown in Figure 3, is formed from a base portion 61 and inclined planar portions 62a and 62b fixed thereon. The base portion 61 has a substantially rectangular bottom portion 61b and upright portions 61c and 61d extending upward from its opposing edges. When the base portion 61 is placed on the first jig 51, one corner 61a of the bottom portion 61b abuts against the inner surface of the L-shaped projection 53. As a result, when the second jig 60 is placed on the first jig 51, as shown in Figure 4, the position of the second jig 60 on the first jig 51 is stably determined. The inclined planar portions 62a and 62b fixed thereon are positioned to extend between the intermediate portion 61e of the bottom portion 61b and the tops of the upright portions 61c and 61d, respectively. The angle between the inclined plane portion 62a and the inclined plane portion 62b is set so that the sample S can be positioned such that the side surface of the sample S abuts against the inclined plane portion 62a and the inclined plane portion 62b, and the wider surface of the sample S extends perpendicularly to the plane direction of the inclined plane portion 62a and the inclined plane portion 62b. Typically, the corners of the sample S are right angles, so the angle between the inclined plane portion 62a and the inclined plane portion 62b may also be a right angle. Furthermore, claw portions 63a and 63b are provided on the edges of the inclined plane portions 62a and 62b that extend in directions that intersect each other, extending perpendicularly upward with respect to the planes of the inclined plane portions 62a and 62b. As shown in Figures 3(C) and (D), when the sample S is placed between the inclined plane portion 62a and the inclined plane portion 62b, the inner surfaces 64a and 64b of the claw portions 63a and 63b come into contact with the surface of the sample S, thereby stably determining the position of the sample S on the inclined plane portions 62a and 62b.

[0020] Referring to Figures 5(A) and (B), when setting the jig 5 on the sample stage 4 and placing the sample S on it, first, the first jig 51 is fastened to the sample stage 4 with screws, and then one corner 61a of the base portion 61 of the second jig 60 is brought into contact with the inner surface of the protruding portion 63 of the first jig 51 (see Figure 4). At this time, it is preferable that the jig 5 is set up so that the plane direction of the inclined plane portions 62a and 62b of the second jig 60 is substantially aligned with the direction of X-ray propagation. After that, the cell S is placed on the inclined plane portions 62a and 62b. At this time, with one corner of the cell in the sample S in the lowest position, the wide surface faces substantially perpendicular to the direction of X-ray propagation, and the edge of one surface contacts the inner surfaces 64a and 64b of the claw portions 63a and 63b of the inclined plane portions 62a and 62b, so that the cell S is always positioned in substantially the same position and orientation with respect to the direction of X-ray propagation.

[0021] As previously mentioned, the sample S may be a single cell or a cell sandwiched between two restraint plates. In Figures 5(A) and 5(B), the sample S is a cell sandwiched between two restraint plates and placed on the jig 5. In this case, cell S1 is sandwiched between restraint plates S2 and S3, and a load cell S5 for detecting the pressure acting on cell S1 is sandwiched between restraint plate S3 and restraint plate S4 located outside of it, and a bolt S6 may be fastened while compressing the space between restraint plate S2 and restraint plate S4.

[0022] Thus, by fixing the jig 5 to the sample stage 4 as described above and placing the sample S, which is cell C, on the jig 5, the cell can always be positioned in the same orientation and location as much as possible with respect to the direction of X-ray propagation.

[0023] Experimental example The following experimental examples have confirmed that by using the jig described above, the cell can always be positioned in the same orientation and location as much as possible with respect to the direction of X-ray propagation. It should be understood that the following experimental examples illustrate the effectiveness of this embodiment and do not limit the scope of the present invention.

[0024] First, the same cell (salt concentration 1M) was repeatedly (N1~N7) placed on a jig fixed to the sample stage of the X-ray inspection system as described above. Each time it was placed, the X-ray transmission intensity was measured, and the salt concentration of the excess liquid was calculated from these measurements. As a result, as shown in Figure 6, the deviation of the calculated salt concentration value CS over the seven trials was 0.08M.

[0025] Next, using the same cells, the position and orientation of the cells were changed by the ranges shown in Table 1, and the changes in the X-ray attenuation rate were detected for each change. From the detected changes in the X-ray attenuation rate, the range of change in the X-ray attenuation rate when the position and orientation of the cells changed by ±1 mm and ±1° was calculated, and the cumulative crossover (square root of the sum of the squares of the rate of change) for changes in the position and orientation of the cells by ±1 mm and ±1° was calculated. [Table 1] As a result, the cumulative crossover for a change in cell position and orientation of ±1 mm and ±1° was 0.011. This value corresponds to a change of 0.11 M in salt concentration. In other words, the deviation of 0.08 M in the calculated salt concentration shown in Figure 6 is smaller than the deviation in salt concentration when the cell position and orientation are changed by ±1 mm and ±1°. Therefore, it was shown that when cells are placed in the jig used in this embodiment, the deviation in cell position and orientation is smaller than ±1 mm and ±1°.

[0026] Thus, according to the method of this embodiment, in a system for inspecting X-ray transmission intensity, the cell is always positioned in substantially the same state on the sample stage, and variations in the X-ray transmission distance in the cell are suppressed, thereby enabling stable detection of the salt concentration of the excess liquid in the cell.

[0027] While the above description is made in relation to embodiments of the present invention, many modifications and changes are readily possible for those skilled in the art, and it will be clear that the present invention is not limited to the embodiments illustrated above, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] A method for detecting the salt concentration of excess non-aqueous electrolyte in a secondary battery cell based on the amount of X-rays transmitted to the excess electrolyte irradiated onto the excess electrolyte, The process of placing a jig on a sample stage positioned between the X-ray source and the X-ray detector, The process of installing the cell on the jig, The process involves irradiating the cell with X-rays from the X-ray source and measuring the intensity of the X-rays that have passed through the excess liquid in the cell using the X-ray detector, A process for detecting the salt concentration of the excess liquid based on the measured X-ray intensity, Includes, The jig on which the cell is installed is A first rectangular flat jig fastened to the sample stage by screws, the first jig having an L-shaped projection formed perpendicular to the surface direction across two intersecting outer edges at one corner, A second jig having a base portion that abuts the inner surface of the L-shaped projection of the first jig, and two flat plate portions formed to extend diagonally upward from the portion between the two opposing edges of the base portion toward the upper part of each of the two edges, wherein the two flat plate portions are oriented such that their surface directions are substantially parallel to the direction of X-ray propagation, and claw portions are formed on the edges of the two flat plate portions that extend in a direction substantially perpendicular to the direction of X-ray propagation, with the claw portion protruding upward. Includes, In the process of setting the cell on the jig, when setting the cell on the second jig, the two intersecting edge surfaces of the cell at one corner are extended along the two flat plate portions of the second jig, and the outer surface of the cell perpendicular to the edge surface, or, when the cell is held between two restraining plates, the outer surface of one of the restraining plates is brought into contact with the claw portion, thereby making the one corner of the cell the lowest point, and maintaining a substantially constant transmission distance of the X-rays passing through the cell.

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